This invention relates to sewing machines, more particularly, to continuous pattern feed elongation in an electronically controlled sewing machine.
In heretofore known sewing machines utilizing a cam device and mechanical linkage to retain and transfer needle position information, it is possible to control the length of the pattern simply by adjusting the stitch length of the sewing machine. However, the amount of elongation possible was limited by the stitch length capability of the sewing machine. In certain sewing machines provision was made for adjustably controlling the rotational speed of the cam. Thus, the cam profile represented a continuous locii of points for needle position, bight and, in some cases, feed direction and rate, as opposed to discrete points on the cam profile representing needle position whenever the cam speed is a fixed ratio of the sewing machine speed. Thus, in these heretofore known mechanical sewing machines pattern elongation was possible merely by increasing the ratio between the sewing machine speed and the cam speed. Such a prior art sewing machine is disclosed in the U.S. Pat. No. 3,291,082 issued on Dec. 13, 1966.
With the advent of the electronically controlled sewing machine, stitch pattern information was retained in a solid state memory. Thus, the relationship of cam speed to sewing machine speed was lost. Normally, a position sensor sensitive to arm shaft rotation triggers the release of information from the solid state memory once during each stitch cycle. By including, in an electronically controlled sewing machine, a needle bar control assembly which permits discontinuing end-wise needle reciprocation while continuing with work feeding operations, pattern feed elongation may be obtained. Such a device is disclosed in U.S. Pat. No. 4,138,955, issued on Feb. 13, 1979 to Garron. In that patent, since a number of needle reciprocations could be discontinued, the pattern could be elongated by integral multiples depending upon the number of stitches skipped.
In the U.S. Pat. No. 4,016,821, issued on Apr. 12, 1977 to Minalga, there is disclosed means for controlling, among other things, the feed in an electronically controlled sewing machine so as to be able to reduce the stitch length derived from the information stored in the solid state memory. U.S. Pat. No. 4,177,744, issued Dec. 11, 1979 to Wurst et al, discloses a digital override control for bight and feed in a sewing machine whereby fixed fractions of the signal derived from the solid state memory may be transmitted to the feed actuator in order to attenuate the signal. The sewing machine disclosed in that patent also has the capability for doubling the feed. Thus, by actuating the digital overrides for feed to fractionate the feed signal derived from the solid state memory and by doubling feed cycle between stitches it is possible to attain pattern feed elongation in discrete steps from 0 to 2 times size. However, a smooth transition over that range is not likely because of the difficulty in selecting the proper digital override for feed multiplication to obtain a uniform change from minimum to maximum.
What is required is a device which will permit a sewing machine operator to readily obtain a uniform progression in pattern feed size from 0 to the maximum multiplication thereof.